Electronic clinical thermometer is currently available which takes a body temperature for a predetermined time interval, calculates a converged temperature value or a predicted body temperature value based on the changes of the measured temperature data, and displays the computed value to reduce the time interval for taking the body temperature. The several sampled temperature data are taken in the reduced short time period, so that the difference between the computed predicted value and the taken temperature value is rather large and the predicted value displayed in the reduced short time interval is unstable and not reliable. Therefore, the conventional electronic thermometer has the disadvantages that the predicted inaccurate temperature on display is misread by an observer of the thermometer as a correct body temperature, which reults in inaccurate measurement.